Recently, acoustic sensors have been used for the non-invasive detection of coronary artery disease. See co-assigned and co-pending U.S. patent application Ser. No. 09/188,510 entitled “Non-Invasive Turbulent Blood Flow Imaging System,” the contents of which are hereby incorporated by reference as if recited in full herein. Generally stated, in operation, sensors are configured on a patient's chest (i.e., contacting the external epidermal surface or skin) to generate an electrical signal in response to a detected acoustic wave. The detected acoustic wave signals are processed to identify features that indicate the condition of a patient's coronary arteries, specifically the presence or absence of lesions that limit the flow of blood through the coronaries. An essentially uniform display indicates normal blood flow, while a non-uniform display may indicate abnormal (turbulent) blood flow and/or the presence of an occlusion.
In the above-described non-invasive systems, the acoustic sensors are positioned over the chest cavity in an acoustic window as described in co-pending and co-assigned U.S. patent application Ser. No. 09/188,434 entitled, “Acoustic Sensor Array For Non-Invasive Detection of Coronary Artery Heart Disease,” the contents of which are hereby incorporated by reference as if recited in full herein. In position, the sensors are preferably configured over the intercostal space so as to reliably generate data signals corresponding to the blood flow of the patient during each phase of the cardiac cycle. The acoustic sensor is preferably designed to sense the flexing of a patient's external epidermal surface (skin) that is a result of the localized nature of the internal heart sounds. The sensor is also preferably easy to position on a patient and inexpensive such that it can be a single use device, which is disposable after use. In operation, the sensor is preferably configured to be conformal to the chest configuration of a patient (which varies patient to patient) and is also preferably configured to generate the electrical signal based on the flexure of the skin. Unfortunately, poor correlation of signals from improper sensor positioning, array geometry, and/or sensor configurations can adversely affect the reliability and/or correlation of the detected acoustic signal. Indeed, one potentially problematic sensor characteristic is that it can generate signals which are not representative of the interested acoustic wave associated with the blood flow of a patient, i.e., it can be responsive to extraneous acoustic waves and noise.
Conventional acoustic sensors can have poor signal to noise ratio (SNR) in that they can be unduly sensitive to environmental noise (typically requiring a special, quiet room be used for acoustic applications) or can suffer from low sensitivity relative to its electrical floor. Other sensors have other performance deficiencies such as inadequate sensitivity. In addition, many sensors are relatively complex configurations which can make them expensive to produce and difficult to apply clinically.
An example of a conventional disposable acoustic pad sensor is illustrated in U.S. patent application Ser. No. 08/802,593. The sensor includes a plurality of layers of various materials connected at one end to a substantially rigid electrostatic shield and electrical connector. Another example of an acoustic sensor is shown in U.S. patent application Ser. No. 09/136,933. This sensor is a flexible thin-film sensor which includes a foot portion and a two-piece piezoelectric film support. Still other examples of acoustic sensors are described in U.S. Pat. Nos. 5,365,937, and 5,807,268. These sensors employ an air gap and a frame which acts to stretch and hold a polymer film in tension. However, there remains a need to provide improved sensors for the efficient and improved passive detection of heart and blood-flow acoustics.